2268 Journal of Applied Microscopy 



the inside of the chamber moist. In this position the seedlings are exactly 

 horizontal. 



Incipient curvature may be observed at the end of 3-5 hours and the retro- 

 gression of the curve during the next 10-24 hours. This will also furnish a 

 means of comparing the region of curvature with the region of growth. 



2. Region of Curvature in Unjointed Stems. Potted plants or cut stems of 

 Vinca major are convenient to use for this experiment. If the latter is selected 



cut off the stem under water, and pass it through a hole in the cork of a bottle 

 of water, packing the stem firmly with cotton batting. Mark the terminal three 

 or four internodes at intervals of 5 mm. and place the stem in a horizontal posi- 

 tion. Make observations as in the previous experiment. 



3. Region of Curvature in Jointed Stems. For this experiment use stems of 

 Tradescantia or of some grass. Remove all the leaves and prepare them in the 

 same manner as in the preceding experiment, except that the stems are marked 

 off at intervals of 2 mm. and two rows of dots are made opposite each other. 



Fig. 12. — A Root growing into Mercury. 



When the stem is placed in the horizontal position one row of dots should be 

 directly below the other. 



This experiment affords a convenient means of demonstrating that these 

 responses are growth curvatures and that the response is manifested only in the 

 growing zone. The marks on the dorsal and ventral sides of the stem show the 

 relative amount of growth on the different sides. 



4. The Position of Greatest Stimulation. The fact that plants respond differ- 

 ently to different degrees of stimulation may be shown by preparing roots as in 

 Experiment 1, and inclining them at angles of 45°, 90°, 135°, and 180° from 

 their normal position. The angle at which the response is first manifested 

 should be carefully noted. 



5. Latent Period. The latent period which elapses between the application 

 of the stimulus and the first response is satisfactorily exhibited by nearly all 

 growing stems. A potted plant or a crock of seedlings growing in earth give 

 the best results. Thrust two slender iron wires into the earth on either side of 

 the stem, giving them the same direction and height as the stem. Turn the 



